1. Field of the Invention
The present invention relates to a double resonant antenna apparatus suitable for use as an built-in antenna of a portable radio unit.
2. Description of the Related Art
As conventional double resonant antenna apparatuses, those disclosed in, for example, Japanese Patent Application Laid-Open Nos. 347507/1993 and 69715/1994 are known. FIG. 12 is a schematic diagram of the antenna apparatus shown in Japanese Patent Application Laid-Open No. 347507/1993. In the drawing, reference numeral 14 denotes a flexible printed wiring board; 15, a feeding element; and 16, a nonfeeding element. FIG. 13 is a schematic diagram of the antenna apparatus shown in Japanese Patent Application Laid-Open No. 69715/1994. In the drawing, reference numeral 17 denotes an inverted-F antenna, and 18 an induction dielectric element.
The double resonant antenna described in Japanese Patent Application Laid-Open No. 347507/1993 has a drawback in that the apparatus assumes a high attitude since it is assumed that the antenna is installed perpendicular to a conductive plate. On the other hand, the double resonant antenna described in Japanese Patent Application Laid-Open No. 69715/1994 has a drawback in that since the inverted-F antenna and a short-circuited end of the inductance dielectric element are on the same side with respect to the antenna, coupling between the two elements is weak.